An analysis of the influence of sex hormones on Balb/c mice infected with Plasmodium berghei

The unique interplay of mitochondrial oxidative phosphorylation (OXPHOS) and immunity and its potential implication for the sex- and age-related morbidity of severe COVID-19 patients

Aged male patients are more vulnerable to severe or critical symptoms of COVID-19, but the underlying mechanism remains elusive. In this study, we analyzed previously published scRNA-seq data from a large cohort of COVID-19 patients, castrated and regenerated mice, and bulk RNA-seq of a RNAi library of 400 genes, and revealed that both immunity and OXPHOS displayed cell-type-, sex-, and age-related variation in the severe or critical COVID-19 patients during disease progression, with a more prominent increase in immunity and decrease in OXPHOS in myeloid cells in the males relative to the females (60-69 years old). Male severe or critical patients above 70 years old were an exception in that the compromised negative correlation between OXPHOS and immunity in these patients was associated with its disordered transcriptional regulation. Finally, the expression levels of OXPHOS and androgens were revealed to be positively correlated, and the responses of macrophages to android fluctuation were more striking than other types of detected immune cells in the castrated mice model. Therefore, the interplay of OXPHOS and immunity displayed a cell-type-specific, age-related, and sex-biased pattern, and the underlying potential regulatory role of the hormonal milieu should not be neglected.

Testosterone induces sexual dimorphism during infection with Plasmodium berghei ANKA

Malaria is the most lethal parasitic disease worldwide; men exhibit higher mortality and more severe symptomatology than women; however, in most studies of immune response in malaria, sex is not considered a variable. Sex hormones 17β-oestradiol and testosterone are responsible for the main physiological differences between sexes. When interacting with their receptors on different immune cells, they modify the expression of genes that modulate cell proliferation, differentiation, and synthesis of cytokines. The immunosuppressive activity of testosterone is well accepted; however, its participation in the sexual dimorphism of the immune response to malaria has not been studied. In this work, we analysed whether altering the concentration of testosterone, through increasing the concentration of this hormone for exogenous administration for three weeks, or gonadectomy before infection with Plasmodium berghei ANKA affects different cells of the immune response necessary for parasite clearance. We also assessed the concentration of pro-and anti-inflammatory cytokines in male and female CBA/Ca mice infected or not with the parasite. Our results show that testosterone changes affect females more than males, resulting in sex-associated patterns. Testosterone administration increased parasitaemia in intact males while reducing it in intact females leading to a dimorphic pattern. In addition, gonadectomy increased parasitaemia in both sexes. Moreover, testosterone administration prevented both weight loss caused by the infection in females and hypothermia in gonadectomized mice of both sexes. Boosting testosterone concentration increased CD3+ and CD8+ populations but decreased the B220+ cells exclusively in females. Additionally, testosterone reduced IFN-γ concentration and increased IL-6 levels only in females, while in males, testosterone increased the number of NK cells. Finally, gonadectomy decreased TNF-α concentration in both sexes. Our results demonstrate that testosterone induces different patterns depending on sex and testosterone concentration. The results of this work contribute to understanding the impact of modifying testosterone concentration on the immune response specific against Plasmodium and the participation of this hormone in sexual dimorphism in malaria.

Dimorphic effect of 17β-oestradiol on pathology and oxidative stress in experimental malaria

Malaria is the parasitic disease with the highest mortality worldwide; males exhibit higher mortality and more severe symptomatology than females, suggesting the participation of sexual hormones in protection and pathology. We have documented that gonadectomy modifies oxidative stress in Plasmodium berghei ANKA-infected mice in a dimorphic manner. However, gonadectomy decreases all sexual steroids levels, making it difficult to determine the contribution of each hormone to the results. This study aimed to explore the participation of 17β-oestradiol (E2) in oxidative stress in the blood, spleen, liver and brain of P. berghei-infected female and male mice. E2 was administered to intact or gonadectomized (GX) male and female mice to assess their effects on parasitaemia, body weight loss and hypothermia. We also measured the effect of E2 on the specific activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) and on malondialdehyde (MDA) levels in the blood, spleen, liver and brain of CBA/Ca male and female mice infected with P. berghei ANKA. We detected the effects of E2 and sexual dimorphism on all tissues and variables analysed. Administration of E2 increased parasitaemia in intact mice. However, reconstitution of GX female mice with E2 decreased parasitaemia. E2 decreased body weight and differentially modulated oxidative stress depending on the sex, infection and tissue analysed. Low antioxidant activity was detected in the brain, suggesting additional protective antioxidant mechanisms in the brain independent of antioxidant enzymes. Our results explained, at least in part, the sexual dimorphism in this experimental model of malaria.

Irradiated sporozoite vaccination induces sex-specific immune responses and protection against malaria in mice

In both preclinical animal studies and human clinical trials, adult females tend to develop greater adaptive immune responses than males following receipt of either viral or bacterial vaccines. While there is currently no approved malaria vaccine, several anti-sporozoite vaccines, including RTS,S/AS01 and attenuated sporozoite vaccines, are in development, but the impact of sex and age on their efficacy remains undefined. To examine sex differences in the efficacy of anti-sporozoite stage malaria vaccination, adult (10 weeks of age) or juvenile (11 days of age) male and female C3H mice were twice vaccinated with irradiated transgenic Plasmodium berghei sporozoites expressing the P. falciparum circumsporozoite (CSP) protein and 45 days post boost vaccination, mice were challenged with transgenic P. berghei via mosquito bite or intradermal challenge. Immunization with irradiated sporozoites resulted in greater protection against challenge in adult females, which was associated with greater anti-CSP antibody production and avidity, as well as greater hepatic, but not splenic, CD8+ T cell IFNƴ production in adult females than adult males. No sex differences in adaptive immune responses or protection were observed in mice vaccinated prior to puberty, suggesting a role for sex steroid hormones. Depletion of testosterone in males increased, whereas rescue of testosterone decreased, anti-CSP antibody production, the number of antigen-specific CD8+ T cells isolated from the liver, and protection following parasite challenge. Conversely, depletion of sex steroids in female mice did not alter vaccine-induced responses or protection following challenge. These data suggest that elevated testosterone concentrations in males reduce adaptive immunity and contribute to sex differences in malaria vaccine efficacy.

Could age and aging change the host response to systemic parasitic infections? A systematic review of preclinical evidence

The impact of age and aging in the evolution of systemic parasitic infections remains poorly understood. We conducted a systematic review from preclinical models of Chagas disease, leishmaniasis, malaria, sleeping sickness and toxoplasmosis. From a structured and comprehensive search in electronic databases, 29 studies were recovered and included in the review. Beyond the characteristics of the experimental models, parasitological and immunological outcomes, we also discussed the quality of current evidence. Our findings indicated that throughout aging, parasitemia and mortality were consistently reduced in Chagas disease and malaria, but were similar or increased in leishmaniasis and highly variable in toxoplasmosis. While a marked humoral response in older animals was related to the anti-T. cruzi protective phenotype, cellular responses mediated by a polarized Th1 phenotype were associated with a more effective defense against Plasmodium infection. Conversely, in leishmaniasis, severe infections and high mortality rates were potentially related to attenuation of humoral response and an imbalance between Th1 and Th2 phenotypes. Due to the heterogeneous parasitological outcomes and limited immunological data, the role of aging on toxoplasmosis evolution remains unclear. From a detailed description of the methodological bias, more controlled researches could avoid the systematic reproduction of inconsistent and poorly reproducible experimental designs.